1. Field of the Invention device of an engine.
2. Description of the Related Art
In a known "air blast" valve, the opening and closing operation of the nozzle opening is electromagnetically controlled by a needle, to cause an injection of fuel by pressurized air. A pressurized air passage extending from the nozzle opening along the needle is formed around the needle and connected to a pressurized fuel source, a nozzle chamber open to the pressurized air passage is provided, and the nozzle of the fuel injector is arranged deep in the interior of the nozzle chamber. The needle has a guide portion formed thereon, this guide portion having three equally spaced lobes which are in slidable contact with the inner wall of the pressurized air passage, to support and guide the needle. Because of the provision of the lobes to support and guide the needle, passages formed between the lobes for the fuel-air charge must have a relatively large cross sectional area, to reduce flow resistance.
After fuel is injected from the fuel injector toward the needle, the needle opens the nozzle opening and the thus injected fuel is injected together with pressurized air from the nozzle opening of the air blast valve (see International Publication No. WO87/00583).
Where, however, passages formed between the lobes for the fuel-air charge have a relatively large cross sectional area, as in the above-mentioned air blast valve, when fuel is injected from the fuel injector toward the needle, most of the fuel injected from the fuel injector passes through passages formed between the lobes and collects in the pressurized air passage, near the nozzle opening, and as a result, the fuel collected near the nozzle opening is forced out as liquid fuel by the pressure of the pressurized air when the needle opens the nozzle opening, and thus a problem arises in that fuel injected from the nozzle opening is not fully atomized and is not completely mixed with the air.